1. Field of the Invention
The invention relates to a device which is connectable to a three-phase supply network, where the device particularly serves to protect the motor or the conductor. Here, power is supplied to a load downstream of the device, e.g., an electric motor, by the device. If a three-phase system is present, for instance, the flow of power occurring across three phases L1, L2, L3 of a supply network to a downstream load can be monitored with the device. In order to analyze the flow of power occurring across the three phases, the device comprises an electronic evaluation unit. Upon the occurrence of a critical state, the device interrupts the flow of power to the downstream load. Devices of this type, such as a circuit breaker, are particularly used in the field of industrial automation technology. A power supply to the internal electronics (e.g., electronic evaluation unit) is required in devices of this type.
1.2. Description of the Related Art
An internal power supply can occur, for instance, via a current converter. The current converter converts an AC current in the primary conductor of a device into a secondary current, which can be used to supply power and to detect current. A current-driven 1-phase power supply is thus possible. However, this principle is disadvantageous with respect to DC operation, lacks a compact design and does not have a low level of cost.
Alternatively, power can be supplied internally via an auxiliary voltage. Here, the required voltage is fed externally via terminals, for instance, is adjusted by an upstream power supply and then supplied to an electronic evaluation units. An AC and DC operation with a compact structure is thus possible. However, this principle is disadvantageous with respect to current detection and does not have low level of cost. Different power supply embodiments are also necessary because the varied voltages in the different systems. Moreover, an additional expense occurs with one user because he requires additional power supply lines and must connect to the device.
In the field of Energy harvesting, single-phase power supplies with step-up converters, which are used to supply power internally, are likewise known. Step-up converters can convert the smallest voltages into usable electronic voltages of a few volts. The disadvantage of these power supplies is in particular the absent, completely galvanic separation between the primary and second side within the device.